PowerPoint Presentationered/ME482/PPT_Lectur… · PPT file · Web view · 2008-10-28+ Hardness...

ME 482 - Manufacturing SystemsME 482 - Manufacturing Systems

Cutting ToolTechnology

by

Ed Red


Objectives• Introduce tool terminology

• Review reasons for tool wear, including failure modes

• Introduce cutting parameters and Taylor’s tool life equation

• Consider a tool life example

• Review tool materials

• Review modern tool technologies (papers)


Cutting tool related terms• Single point versus multiple point

• Cratering –wear that forms a concave region on the tool

• Tool life – length of cutting time that a tool can be used

• Toughness – capacity to absorb energy without failing

• Hot hardness –capacity to retain hardness at high temperatures

• Cermet – combination of TiC, TiN, TiCN (CN = carbonitride), with nickel and/or molybdenum as binders

• Chip breaker – geometry designed into tool to break stringy chips

• Cutting fluid – Any liquid/gas applied to improve cutting performance


Tool wear• Abrasion - dominant cause of flank wear

• Adhesion – high pressure localized fusion and rupturing

• Diffusion – Loss of hardening atoms at tool-chip boundary (contributes to crater wear)

• Plastic deformation – contributes to flank wear

• Three pronounced wearing regions


Tool lifeTool life – length of cutting time that a tool can be used or a certain flank wear value has occurred (0.02”)

Taylor’s tool life equation:

v Tn = C (exponential again!)

v = cutting speedn = cutting exponentC = cutting constant

Note: n and C depend on speed, work material, tool material, etc. C has units of fpm and is the speed at which the tool life lasts 1 min, i.e., v Tn = C (1) n = C .

For turning at feed = 0.01”/rev. and depth = 0.100 “For turning at feed = 0.01”/rev. and depth = 0.100 “


Operator’s tool lifeTool life is measured by:

• Visual inspection of tool edge• Tool breaks• Fingernail test• Changes in cutting sounds• Chips become ribbony, stringy• Surface finish degrades• Computer interface says

- power consumption up- cumulative cutting time reaches certain level- cumulative number of pieces cut reaches certain value


Tool life exampleThe n and C values in Table 23.2 in the text are based on a feed rate of 0.01 in./rev and a depth of cut of 0.10 in. Determine and compare the cubic inches of steel removed for each of the following tool materials if a 15 minute tool life is required in each case: a) HSS b) ceramic

Solution:

Approach is to determine the MRR = v f d. We are given the feed rate and the depth of cut; thus, need to calculate the cutting speed.

Given Taylor’s equation and the n and C values, we can solve for v and thus determine the MRR.

Given the MRR, we multiply it by the cutting time to get the volume of material removed.


Tool life exampleSolution for HSS:

From Table 23.2, n = 0.125 and C = 200 ft/min (for steel cutting)

From v Tn = C we solve for v:

v = 200/(15)0.125= 142.6 ft/min

Now, get the MRR:

MRR = (142.6) (12) (0.01) (0.10) = 1.71 in3/min

Volume removed in 15 min is (15) (1.71) = 25.66 in3


Tool life exampleSolution for ceramic:

From Table 23.2: n = 0.6 and C = 10,000 ft/min

From v Tn = C we solve for v:

v = 10,000/(15)0.6= 1969.5 ft/min

Now, get the MRR:

MRR = (1969.5) (12) (0.01) (0.10) = 23.63 in3/min

Volume removed in 15 min is (15) (23.63) = 354.5 in3

Ceramic about an order-of-magnitude more effective than HSS!


Cutting tool materials

• Plain carbon and low alloy steels – rarely used today

• High-speed steel (HSS) – primary alloys are tungsten (AISI T grade > 12%) or molybdenum (M grade, 5 – 8%).... sometimes coated with TiN to improve performance, toughness good

• Cast cobalt alloys – cobalt (50%), chromium (30%), and tungsten (20%), improved wear resistance, but toughness < HSS

+ Hardness+ Hardness


Cutting tool materials• Cemented carbides, cermets, and coated carbides – related

materials that are a composite of ceramic and metallic materials. Cemented carbides use tungsten carbides….cermets use titanium carbides. Coated carbides use coatings of TiC or Al2O3 to improve wear properties. Higher WC contents in cemented carbides detrimental to steel cutting (affinity of steel with carbon in WC), but ok for other metals. Alloying with TiC and TaC reduces this problem.

• Ceramics – Primarily Al2O3... not good in dynamic (higher speeds, shock) cutting situations.



Cutting tool materials

• Synthetic polycrystalline diamond (SPD) and cubic boron nitride (CBN) – typically used as coating on base tool material such as WC-Co…there is an affinity of SPD with iron and nickel; CBN does not have this affinity… expensive.



Cutting tool materials – HSS alloyingElement Properties

Tungsten Increases hot hardnessHard carbides formed, improving abrasion resistance

Molybdenum Increases hot hardness Hard carbides formed, improving abrasion resistance

Chromium Depth hardenability during heat treatHard carbides formed, improving abrasion resistanceSome corrosion resistance

Vanadium Combines with carbon for wear resistanceRetards grain growth for better toughness

Cobalt Increases hot hardness, toughness

Carbon Hardening elementForms carbides


Cutting tool materialsMost modern cutting tool materials are a matrix of materials designed to be very hard. Important terms are toughness, hardness and hot hardness. Note that the rake angle is chosen small (near 0 deg) for the harder, more brittle tool materials to keep the tool in compression.

U (Specific Energy) is a measure of toughness, while the table shows typical hardness values at room temperature for cutting tool materials. The figure shows how hardness degrades with increasing temperature.


Cemented carbide classification

C1 Roughing C5

C2 General purpose C6

C3 Finishing C7

C4 Precision finishing C8

Non-steel cutting Steel cutting

Al, Cu, Brass, Ti

Cast iron

Abrasive wear resistance

Crater wear resistance

Wea

r res

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Toug

hnes

s

% T

iC fo

r ste

el c

uttin

g gr

ades

% C

obal

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No TiC, TaC Contain TiC, TaC


Cutting tool geometry

7 elements of a single point tool geometry


Milling tool geometry

Face cutter

Chamfering cutter


Cutting tool geometry

Mini-cutters

Coated tools


Cuttingfluids

Lubricants – purpose is to reduce friction… usually oil based

Coolants – purpose is to transport heat… usually water basedBoth lose their effectiveness at higher cutting speeds!


High speed machining characteristicsQuestion – does Taylor’s equation even apply for HSM?

> 500 linear in/min

spindle speeds > 10,000 rpm

surface cutter speeds > 1200 ft/min

spindles in the 50 hp range

head tilt speeds > 1000 deg/min

balanced tool holders

problems with tool deflection

must operate within machine harmonics


High speed machining at Remmele

Remmele's High Speed and High Velocity technology provide distinct advantages in increasing product performance.

•Weight Reduction (thin walls to 0.010"/0.25mm) •Time Savings •Reduced Distortions and Warping

High Speed Machining is high volume metal removal within a range of high surface-cutting speeds (feet per minute) and feeds (in/min).

High Velocity Machining exhibits significant reduction in machining forces and power absorption, and dramatically shifts the heat energy distribution from the cutter/workpiece to the chip.


Cutting tools review questions: Of the following cutting conditions, which one has the greatest

effect on tool wear? (a) cutting speed, (b) depth of cut, or (c) feed.

As an alloying ingredient in high-speed steel, tungsten serves which of the following functions (more than one answer)? (a) forms hard carbides to resist abrasion, (b) improves strength and hardness, (c) increases corrosion resistance, and (d) increases hot hardness.

Cast cobalt alloys typically contain which of the following main ingredients (more than one answer)? (a) aluminum, (b) cobalt, (c) chromium, (d) nickel, and (e) tungsten.

Answer: (a)

Answer: (a), (b), (d)

Answer: (b), (c), (e)


Cutting tools review questions: Which of the following is not a common ingredient in cemented

carbide cutting tools (more than one answer)? (a) Al203, (b) Co, (c) CrC, (d) TiC, and (e) WC.

An increase in cobalt content has which of the following effects on WC-Co cemented carbides (one best answer)? (a) decreases transverse rupture strength, (b) increases hardness, (c) increases toughness.

Steel cutting grades of cemented carbide are typically not characterized by which of the following ingredients (more than one answer)? (a) Co, (b) Ni, (c) TiC, (d) TaC, and (e) WC.

Answer: (a), (c)

Answer: (c)

Answer: (b)


Cutting tools review questions: Which of the following processes are used to provide the thin

coatings on the surface of coated carbide inserts (more than one answer)? (a) chemical vapor deposition, (b) electroplating, (c) physical vapor deposition, or (d) pressing and sintering.

Which of the following materials has the highest hardness? (a) aluminum oxide, (b) cubic boron nitride, (c) high speed steel, (d) titanium carbide, or (e) tungsten carbide.

If you had to select a cemented carbide for an application involving the finish turning of steel, which of the following grades would you select (one best answer)? (a) C1, (b) C3, (c) C5, or (d) C7.

Answer: (a), (c)

Answer: (b)

Answer: (d)


Cutting tools review questions: Which of the following are the two main functions of a cutting

fluid in machining (two answers only)? (a) improve surface finish on the workpiece, (b) reduce forces and power, (c) reduce friction at the tool-chip interface, (d) remove heat from the process, and (e) wash away chips.

Answer: (c), (d)

PowerPoint Presentationered/ME482/PPT_Lectur… · PPT file · Web view · 2008-10-28+ Hardness...

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